AS Path Attributes

1. Attribute Categories
   1. Well-Known, Mandatory
   2. Well-Known, Discretionary
   3. Optional, Transitive
   4. Optional, Non-Transitive
2. The Attributes
   1. Weight
   2. Origin
   3. Metric
   4. Local Preference
   5. AS Path
   6. Multi-Exit Discriminator
   7. Next Hop
   8. Community
   9. Aggregator
   10. Atomic Aggregate
   11. Cluster List

 

Attribute Categories

1. Well-Known, Mandatory
2. Well-Known, Discretionary
3. Optional, Transitive
4. Optional, Non-Transitive

Well-Known, Mandatory

Well-known, Mandatory attributes must appear in every UPDATE message. It must be supported by all BGP software implementations. If a well-known, mandatory attribute is missing from an UPDATE message, a NOTIFICATION message must be sent to the peer.

Examples:

• AS_path
• ORIGIN
• NEXT_HOP

Well-Known, Discretionary

Well-Known, Discretionary attributes may or may not appear in an UPDATE message, but it must be supported by any BGP software implmentation.

Examples:

• LOCAL_PREF
• ATOMIC_AGGREGATE

Optional, Transitive

Optional, Transitive attributes may or may not be supported in all BGP implementations. If it is sent in an UPDATE message, but not recognized by the receiver, it should be passed on to the next AS.

Examples:

• The Aggregator of the Route ( AGGREGATOR)
• Community String (COMMUNITY)

Optional, Non-Transitive

Optional, Non-Transitive attributes may not be supported and will not be passed on if advertised.

May or may not be supported, but if received, it is not required that the router pass it on. It may safely and quietly ignore the optional attribute.

Examples:

• Multi-Exit Discriminator (MULTI_EXIT_DISC)
• Route Originator ID (ORIGINATOR_ID)
• Route Cluster List (Cluster List)

BGP AS-Path Attributes

 

 

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